1. Field of the Invention
The present invention relates to a semiconductor device wherein the laminated structure of nitride semiconductors is formed, and more specifically, to a semiconductor device that can ensure sufficient capacitance and withstand voltage without enlarging a chip area.
2. Background Art
A nitride semiconductor is the generic term for gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InM), and mixed crystals composed of these nitrides. Generally, the nitride semiconductor is mechanically robust and chemically stable, and has high thermal conductivity and excellent heat dissipation properties. Therefore, a semiconductor element fabricated using a nitride semiconductor multilayer film structure, for example, an AlxGa1-xN/GaN high electron mobility transistor (HEMT) is considered to be applied to a high output high-frequency element. Therefore, a large number of trial products of AlGaN/GaN HEMTs have been reported.
A circuit using an AlGaN/GaN HEMT can be used as a monolithic microwave integrated circuit (MMIC) in the same way as other high-frequency transistors. For fabricating an MMIC, the structure and the fabricating method of passive elements, such as a resistor, an inductor, and a capacitor, other than transistors are important. In conventional metal insulator metal (MIM) capacitors, a silicon nitride (SiNx) film is deposited on an underlying metal layer by a chemical gas-phase growing method, and is used as an insulating film.
The breakdown electric field of the SiNx film is not more than about 6 MV/cm (for example, refer to N. Inoue, Ippei Kume, Jun Kawahara, Shinobu Saito, Naoya Furutake, Takeshi Toda, Koichiro Matsui, Takayuki Iwaki, Masayuki Furumiya, Toshiki Shinmura, Koichi Ohto, and Yoshihiro Hayashi, Jpn. J. Appl. Phys. 46, 1968 (2007)). Therefore, the breakdown voltage of an MIM capacitor using a normal SiNx film of a thickness of 150 nm is about 90 V, and is insufficient for withstanding voltage as a capacitor for the MMIC of an AlGaN/GaN HEMT. When the SiNx film is thickened in order to make the break down voltage higher, the capacitance is lowered in proportional to the film thickness; therefore, the area of the capacitor must be enlarged. If the sufficient capacitance and withstand voltage are to be ensured, a problem of enlarged chip area is caused.